1. Field of the Invention
The present invention relates to a half-wave rectifier circuit for obtaining a DC voltage depending on the level of an AC input signal. A circuit for adjusting an output depending on an AC input signal level, such as a compander (compressor/expander) or ALC, etc., requires a half-wave rectifier circuit for obtaining a DC voltage depending on an AC input level.
Such half-wave rectifier circuit receives an input signal via a coupling capacitor in order to remove any DC component in the input signal. The use of this capacitor results in the generation of an offset voltage, an error in the output of the half-wave rectifier circuit. When the input signal is a low level signal, the error becomes relatively large. Therefore, a half-wave rectifier circuit in which the offset voltage generated by a coupling capacitor does not influence the output is needed.
2. Description of the Related Art
In an existing half-wave rectifier circuit, an input AC signal voltage input via a capacitor to a comparator and a switch circuit. An output of the switch circuit is then supplied to a smoothing circuit. The comparator compares an input signal with the reference voltage and outputs a signal for driving the switch circuit depending on the polarity of the input signal. The switch circuit responds to the output of the comparator to connect the input signal to the smoothing circuit when the polarity of input signal is positive (+) or to the ground when the polarity is negative (-). As a result, a half-wave rectified voltage is output from the smoothing circuit.
In this existing half-wave rectifier circuit, an offset-voltage appears on the capacitor provided to remove any DC component in the input signal and the offset-voltage affects output voltage. Therefore, such existing half-wave rectifier circuit cannot provide an accurate smoothed output due to the influence by the offset voltage and particularly cannot provide an accurate output when the input level is small because the relative error between the signal voltage and the offset voltage becomes large.